Treatment of synthetic filaments



} Jam 30, 1968 R.W.CHIDGEY ETAL TREATMENT OF SYNTHETIC FILAMENTS Original Filed Nov. 12, 1963 INVENTORS RONALD w. CHIDGEY CLAUDE M.IRWIN PAUL E. SIKORSKI /W ATTORNEY United States Patent 8 Claims. (Cl. 57-157) This application is a division of application Ser. No. 322,704, filed Nov. 12, 1963.

This invention relates to treatment of synthetic fila ments. More particularly, the invention relates toga process and apparatus for treating untwisted nylon filament yarn to relax some and to render same adaptable for use as warp yarn in fabric construction.

Normally, producers of man-made filament yarns employ twisters to impart true twist in the yarns so that the yarns can bev handled conveniently by throwsters and fabric manufacturers without individual filaments becoming separated from the main filament bundle. Twisting the yarn to maintain its unitary and to prevent separation of the individual filaments is an expensive operation. Furthermore, at todays high rate of filament production, especially where the filaments are spun and drawn without intermediate packaging, the yarns cannot be twisted to the desired amount because of mechanical limitations of known twist-imparting devices at extremely high take-up speeds but must be wound up with very little or no twist.

Heretofore several ways have been suggested for treating untwisted filament yarns so that they will perform in a manner comparable to twisted yarn. A recent disclosure describes a process of whipping running yarn of zero or low twist in a confined zone under some tension by perpendicular impingement of a small stream of gas moving at a high velocity. The whipping action causes :he filaments to become interlaced and intertwined. While such yarn processes into fabric as one having considerable twist, the interlaced yarn exhibits very irregular light rellectances because large and small groups of the filaments become erratically entangled. This irregular light reflecting phenomenon is referred to as flashes and is quite undesirable from an aesthetic standpoint. Various resins, potentially resinous materials, adhesives and sizes have been applied to spun yarns or zero twist filament yarns to insure adequate handling characteristics without too much success. These known bonding agents adversely affect the dyeing and tactile properties of the yarn and fabric made therefrom.

Nylon filaments and filaments of other synthetic thermoplastic polymers after being spun have relatively low tensile strength and low molecular orientation. To orient these filaments molecularly and thereby to increase the strength thereof, the filaments are stretched a desired amount by attenuating them using thread advancing devices operated at a predetermined peripheral speed differential therebetween. The drawn filaments are placed under considerable stress during the stretching operation. Most of this stress is relieved in the form of an immediate elastic recovery when the tension on the filament is first reduced. The elastic recovery ordinarily occurs between the drawing device and the yarn take-up device by significantly reducing the tension on the filaments at this point in the drawing operation. The elastic recovery is manifested by a quick reduction in length of the filamerits. Usually, this reduction in length may vary from four to eight percent of the length of the drawn filaments, depending upon processing conditions employed.

In addition to the tendency of the filaments to contract quickly after being drawn, the filaments have a latent overstrain that is slow to be relieved a room temperature. It may take as long as twenty-four hours at room temperature to relieve this strain completely even when the filameris are under little or no tension. I has long been recognized that relief of the latent strain can be hastened by relaxing nylon filaments and filaments of other synthetic thermoplastic polymers at elevated temperatures which causes longitudinal shrinking of the filaments by an additional amount. Hot relaxing has been accomplished by steaming the filaments or by applying heat to the filaments in other ways immediately after drawing and before package formation. Unfortunately, complete relaxation of the filaments ordinarily is gained at the expense of obtaining filaments having an undesirably low initial modulus. In recent times methods and apparatus have been disclosed whereby freshly drawn nylon filaments are hot relaxed under controlled conditions without considerable lowering of the initial modulus thereof. The known methods and apparatus for doing this require extensive alteration of existing nylon drawing equipment and do not permit accurate control of the filaments during hot relaxation thereof so as to produce filaments of optimum physical properties.

It is an object of the present invention to provide a substantially untwisted synthetic continuous multifilament yarn having an undividedness or coherence such that it can be used in the untwisted condition as warp and/or filling yarn of a fabric.

It is another object to provide fabric, the warp and/or" filling of which is constructed from filament yarn treated by the process of the invention.

It is another object of the present invention to provide a process for treating untwisted synthetic continuous multifilament yarn to relax same and at the same time to render same adaptable for use as warp and/or filling yarn of a fabric.

It is a further object of the present invention to provide apparatus for treating untwisted continuous multifilament yarn to relax same and at the same time render the yarn adaptable for use as warp and/ or filling yarn of a fabric.

In accordance with the invention a particular uncrimped continuous multifilament yarn made of a synthetic thermoplastic polymer is provided. The individual filaments of the yarn are in substantially parallel contiguous relation with little or no twist imparted therein. The individual filaments are cohered or attached together at random points to impart a simulated unifilar character thereto and are arranged to render compact transverse rotundness to the yarn. In addition, the yarn can be relaxed or stressrelicyed so as to be mitigated against a latent tendency to retract.

The yarn usually is not crimped; that is, the filaments of the yarn are substantially straight and unbent and have not been textured or otherwise deformed to increase the bulk thereof. The individual filaments are substantially parallel which means they do not criss-cross to a large extent and are not interlaced which would disturb the parallelism of zero twist filaments. The ya-rn can be relaxed, thereby having reduced tendency to contract in length. Being thus treated, the yarn exhibits low shrinkage and relatively high initial modulus. The yarn is not ribbon.- like or pronouncedly flat-sided but rather has a transverse rotundness as a threadline of normal untreated man-made filaments.

In the method of the invention synthetic continuous filament yarn traveling longitudinally from a source of supply is stretched in a zone several times the original length thereof. Thereafter a peripheral effort is applied to the yarn to impart a slight false twist thereto with the twist running back toward the stretch zone. The amount of false twist will be about 2 to 20 turns per inch.

Patented Jan. 30, 1968 if While so twisted, a small amount of liquid evanescent solvent of the polymer from which the yarn is made is applied to the yarn. Just forward of the point of false twist application the yarn detwists and is heated, preferably under low tension, such that the action of the solvent is dissipated. Low tension permits the yarn to relax. Thereafter the yarn is collected in orderly form.

One form of apparatus for treating filaments in the multistage operation herein described includes suitable means for longitudinally forwardly molecularly orientable (undrawn) filament yarn from a suitable source at a predetermined rate. A driven draw roll is positioned in the yarn path and is adapted to forward the yarn at a speed such that the yarn is stretched a desired amount between the forwarding means and the draw roll. Disposed in the yarn path therebetween is a yarn snubbing pin to apply a selected resistance to the forward move ment of the yarn so that the point of stretching of the filaments is localized. A freely rotatable separator roll is positioned adjacent the draw roll in spaced relationship therewith. The axis of the separator roll is at a slight angle with respect to the al'is of the draw roll in order that yarn normally progressing around the draw roll and the separator roll moves in a helical path. Also mounted adjacent the draw roll in spaced relationship therewith in the yarn path is a rotatable yarn heating element having a circumferential flange. The yarn is heated to an elevated temperature by contact with this element after it has been drawn. The flange is adapted to exert a peripheral effort on the yarn so as to impart a slight false twist thereto. The element preferably is a heated roll positioned axially at a slight angle with respect to the axis of the draw roll in order that the yarn normally progressing around the draw roll and the heated roll moves in a helical path. In the yarn path between the draw roll and the flange where the yarn has a slight false twist, means for applying a small amount of a liquid evanescent solvent is positioned. Means for taking up the yarn in a orderly manner is provided without subjecting the yarn to high tension. In the yarn path befdre the take-up means, means for applying a finish or lubricant can be employed.

In accordance with a more specific method of the present invention, undrawn filament nylon yarn is longitudinally forwarded to a stretch zone to increase the orientation of the molecules thereof. During the stretching the temperature of the yarn is raised to about 150490 C. The molecular friction during the necking down of the filaments in drawing plus the surface friction between the snubbing pin and the yarn at the speeds ordinarily employed are sufficient to increase the temperature of the yarn to this range. At low speeds where friction heat may not be sufficient, the snubbing pin can be positively heated, such as by providing an electrically resistant element inside the snubbing pin. During drawing the filaments are subjected to high tensioning. In the next step of the invention, the yarn is cooled to about 40-145 C. and the tension on the yarn is reduced. This can be accomplished by multi-warps of the yarn around the driven draw roll and the separator roll. Three, four, or more wraps are sufficient to provide sufficient gripping of the yarn during the drawing thereof and to provide sutiicient reduction of tension thereon. As is known, the tension on the yarn diminishes as the number of wraps increases. By passing the yarn through the ambient air and in contact with the draw roll and the separator roll, heat is transferred from the drawn yarn so that the yarn is cooled to the required temperature.

A rotational moment is imparted to filaments to false twist the yarn slightly. As indicated above, the amount of twist will be only 2-20 turns per inch. While having this twist, a liquid evanescent solvent is applied to the yarn in a small amount. Ordinarily about 0.2-5.0 percent of the solvent is sufficient to effect sufficient integrality or cohesion of the filaments, although more or lesser amounts of solvent may be employed depending on the type of yarn, type of solvent, degree of cohesion desired, etc.

Next, the yarn is detwisted and heated quickly to about ISO-190 C. to dry the yarn and to deactivate the action of the solvent while the yarn is under reduced tension permitting relaxation thereof. Heating is accomplished by passing the yarn in contacting engagement witl". a heated surface having a peripheral speed substantially equal to the speed of the yarn. The time during which the yarn is heated by the surface is from about 0.001 to 0.4 second, preferably from 0.001 to 0.05 second. This yarn is moved in a figure of eight path, the heating of the yarn by means of the heated surface to the temperature of about 150-190 C. being effected on the inside of the loop of the figure of eight path wherein the yarn moves in a direction opposite to that taken by the yarn around the rolls.

Then, the yarn is cooled quickly to about 40-130 C. The cooling of the yarn is preferably accomplished as it moves in the.loop of the figure of eight path wherein the yarn moves in the same direction as that taken by the yarn around the draw roll and separator roll.

In the next step the yarn again is heated quickly to about 150-490 C. This is accomplished by passing the yarn again in contacting engagement with the same or different moving heated surface. The time during which the yarn is heated by the surface is from about 0.001 to 0.4 second, preferably from 0.001 to 0.05 second. Preferably, the yarn is looped back so that heating thereof is effected again on the inside of the loop of a figure of eight path wherein the yarn moves in a direction opposite to that taken by the yarn around the draw roll and and separator roll.

Finally, the yarn is cooled while the yarn is under a tension of about 0.02-0.2 gram per denier; the heat can be dissipated to the ambient air and to the rolls. Thereafter, the yarn is taken up in an orderly manner in package form under a tension of about 0.05-0.4 gram per denier at a speed of about four to twelve percent less than the speed of the yarn immediately after it is drawn. The yarn can be wound on a bobbin or the like. Before take-up a finish, lubricant or like beneficiating agent can be applied to the yarn to improve its handling characteristics. The yarn even though not twisted can be employed in the warp or filling of woven fabric as similar yarn having considerable twist.

The invention is further illustrated by reference to the accompanying drawing wherein:

The single figure is a schematic view in perspective with principal parts in location illustrating one yarn lacing arrangement employing the apparatus of the invention.

With reference to the drawing, it will be noted that yarn I which is to be treated and which is composed of a bundle of smooth substantially parallel filaments that have not been fully oriented, is supplied from a yarn source. The yarn source can be, for example, a package previously doffed from a conventional filament spinning machine. Also, the apparatus as illustrated can be adapted readily for processing continuous filament yarn which is supplied directly from the spinning machine without an intermediate take-up. The yarn is passed to a rotatably arranged thread advancing means comprising a pair of feed rolls 2, at least one of which is positively driven. The rolls engage each other to nip the yarn sufficiently to prevent slippage of the yarn therebetween. The yarn is led around a snubbing pin 3 or like yarn braking means. The pin preferably is mounted to be non-rotative and has a smooth yarn contact surface made of material having a high resistance to wear. As indicated above, the pin can be heated if needed to raise the temperature of the yarn to the required temperature, although positive heating of the pin is not necessary normally.

After being passed around pin 3 a desired number of times, yarn 1 is directed around a rotatably mounted draw roll 4 and its associated separator roll 5 which is freely rotatably mounted. Roll 4 is positively driven at a peripheral speed such that the yarn is given a predetermined stretch between rolls 2 and 4 which define a stretch zone. As illustrated, the yarn takes five wraps around rolls 4 and 5, the axes of which are asitew so as to permit longitudinal advancement of the yarn from inside to outside of the roll and to prevent superimpositioning of the wraps. This number of wraps normally provides sufficient gripping action so that the yarn is stretched as desired without yarn slippage. As it moves away from pin 3, the yarn normally has an elevated temperature and is under a high tension depending upon the ultimate denier and elongation of the yarn. As the yarn progresses along rolls 4 and 5 the yarn is cooled; and the tension on the yarn is gradually reduced with each succeeding wrap.

A freely rotatable heated yarn relaxing roll 7 having a flange 6 is positioned adjacent draw roll 4 in spaced relationsbip therewith. The axis of roll 7 is at a slight angle with respect to the axis of the draw roll in order that the yarn wraps do not become superimposed. Embedded in roll 7 is an electric resistance heater element (not shown). Lines 7a supply electrical energy to the heater element. The heating of roll 7 can be achieved in other ways, such as by heated fluid inside the roll or by the use of high frequency heating. After completion of the wraps around rolls 4 and 5, the yarn is moved at an angle away from the wraps in a figure of eight path in a reverse wrap about rolls 4 and 7. In the angled path the yarn frictionally engages flange 6 which imposes a peripheral effort thereon such that a slight false twist is imparted to the yarn with the twist running back toward roll 4. While twisted a liquid evanescent solvent is applied to the yarn as it brushes across the surface of wick material 8. The solvent is supplied thereto through conduit 9 from a suitable source (not shown). Usually the solvent will be ietered to insure uniform application thereof to the yarn.

While the yarn is looped back around rolls 4 and 7 the yarn contacts the heated moving surface provided by roll 7, the yarn moving in a direction opposite to that taken by the yarn in its wraps about rolls 4 and 5. During its contact with roll 7 the temperature of the yarn is raised,

the yarn detwists, and the yarn is dried to dissipate the action of the solvent.

The yarn is again cooled. This can be accomplished by completing the figure of eight path of the yarn around roll 4, the heat being transferred to the ambient air and to the roll. The yarn is again looped back and moved in contacting engagement with roll 7 to reheat the yarn. T third heating by contacting roll 7 and intermediate cooling of the yarn is advantageous to insure better relaxation and to insure dissipation of the action of the solvent.

The yarn is then forwarded to a take-up device. Between roll 7 and the take-up device the yarn is cooled. Roll 10 serves as a convenient guide for the yarn moving to the take-up device. One such device is a conventional winder having a drum traverse 11 wherein the yarn is wrapped on a holder 12 to form a package 13 without twist being imparted to the yarn. The yarn may be taken up while being twisted, although twisting of the yarn is not required. The yarn is taken up at speeds permitting reduction in length of the yarn of about four to twelve percent between roll 10 and the point of maximum stretch of the yarn which occurs in the yarn path between pin 3 and roll 4. Yarn forwarding rolls may be interposed in the yarn path beyondroll 1t] and before the point where the yarn is taken up in order to provide better tensioning control.

As illustrated after treatment and 'before take-up of the yarn. a finish, lubricant or like agent can be applied to the yarn to improve the handling properties thereof. This can be accomplished by the provision of wick appli cator 14 having a beneficiating agent supplied thereto through conduit 15 from a suitable source not shown. For best results only a small amount of finish or like agents is present on the yarn prior to treatment. It has beenfound that an excess amount of such agents on the yarn prior to treatment can interfere adversely with the efficacy of the solvent. Conversely, the solvent may destroy the benefits desired from such agents when the solvent is after applied.

Obviously, tension control mechanisms responsive to variations in yarn tension can be employed to vary appropriately the speed of the yarn forwarding devices to provide better control of the yarn. being processed.

The method of the present invention is applicable to a wide variety of synthetic continuous filament yarns. The yarn is made from thermoplastic fiber-forming resins and can be extended by drawing and then shown increased molecular orientation along the axis thereof. The yarn may be formed from these resins by known techniques, including melt extrusion, wet spinning and dry spinning. As examples of the fiber-forming synthetic polymers the following may be mentioned: polyethylene; polypropylene; polyurethanes; copolymers of vinyl acetate and vinyl chloride; the copolymers of vinylidene chloride and a minor proportion of mono-olefinic compounds copolymerizable therewith, such as vinyl chloride, homopolymers of acrylonitrile, copolymers of acrylonitrile and a minor proportion of at least one mono-olefinic compound copolymerized therewith and polymer blends containing polymerized acrylonitrile in a major proportion; copolymers of vinyl chloride and acrylonitrile; linear polyesters of aromatic diearboxylic acids and dihydric compounds, such as polyethylene terephthalate; linear polycarbonamides such as, nylon-66, nylon-6, nylon-4, nylon-7, ny- Ion-610 and other fiber-forming copolymers, e.g. 6/ 66, 6/610/66, 66/610, etc. i

Filaments having a normal cross section such as that obtained using a circular spinning orifice during filarrent formation can be treated. However, multi-lobal yarn and yarn having an axial passage can likewise be treated in accordance with the present process.

Yarn having some twist can be processed. However, it is preferred to start with a source of yarn having zero twist, since an advantage of the present invention is that the need of twist for rendering the yarn processable into fabric is obviated. For economic considerations twist in the yarn to be processed is avoided. The denier of the yarn can vary as well as the denier of the individual filaments, the ordinary deniers of commercially available yarns being completely suitable.

The evanescent solvents are active so as to soften the yarn and to render the same stickable at the temperatures employed. The solvents can be composed of an active substance normally solid at room temperature but readily dissolvable in an inert volatile diluent to form a I single phase liquid. When the yarn carrying the solvent is heated, the diluent flashes therefrom and the action of the active substance is dissipated. Specific solvents will be selected with regard to the type of yarns being processed.

For treating nylon yarns, solutions of multi-hydroxybenzenes have been found to be effective evanescent solvents. Dihydroxybcnzene compounds which can be cmploycd as the active substance in the solvents include resorcinol. hydroquinone and pyrocatechol. A trihydroxybenzene, for example, is pyrogallol. The multi-hydroxybenzencs are not limited to the foregoing specific compounds since derivatives thereof can also be used to effect cohesion and the stabilization of the yarn. The preferred procedure is to dissolve the compounds in a suitable inert diluent. Dihydroxybenzenes and trihydroxybenzenes are readily soluble in water, common alcohols (methanol, ethanol, etc.) and common ethers (dimethyl ether, diethyl ether, etc.). It has been found] that a preferred procedure involves dissolving a predetermined amount of the benzene compound in water or methanol. An aqueous or methanolic solution containing about 5-80 percent dihydroxybenzene or trihydroxybenzcne on a weight basis gives good results. The preferred concentration is 30-40 weight percent. The concentration of the active substance in the evanescent solvent will depend on many factors,

such as the characteristics of the particular substance employed, the amount of liquid placed on the nylon yarn, the polymeric structure of the yarns, etc.

Another effective evanescent solvent for use in treating nylon yarns is molten chloral hydrate or a solution thereof. Chloral hydrate is also readily soluble in water, common alcohols (methanol, ethanol, etc.) and Common ethers (dimethyl ether, diethyl ether, etc.). A preferred procedure involves dissolving a predetermined amount of chloral hydrate in water or methanol. An aqueous or methanolic solution containing about: 25-:9 weight percent chloral hydrate gives good results. The preferred concentration of chloral hydrate in solution is 4085 weight percent.

For treating acrylic filament yarns (yarns made from acrylonitrile polymers) solutions of aliphatic cyclic carbonates are effective evanescent solvent. These carbonates can be selected from the group of the cyclic carbonates of l,2-; 2.3-; and 1,3-dihydric aliphatic alcohols. Such aliphatic cyclic carbonates include ethylene carbonate, propylene carbonate, trimethylene carbonate, 1,2-butyl cue carbonate, l,3-butylene carbonate. 2,3-butylen'e carbonate, isobutylene carbonate and mixtures thereof. Especially useful of the foregoing group is ethylene carbonate. An aqueous solution containing about -?0 percent aliphatic cyclic carbonate on a weight basin gives good results. The preferred concentration of aliphatic cyclic carbonate is 40-60 weight percent.

The following examples will serve to illustrate the invention, although they are not intended to be limitative thereof.

Example I An untwisted, undrawn filament nylon-66 yarn with a spun denier of 190 and composed of 34 filaments was removed axially from a spin bobbin and was advanced by means of a pair of feed rolls as shown in the drawing. The yarn was wrapped two times around snubbing pin 3 and then was wrapped four times around draw roll 4 and separator roll 5. The draw ratio employed was 2.7 and the peripheral speed of the draw roll was 800 yards per minute. The yarn was then wrapped around heated roll 7 and brought at an angle across flange 6 which imparted a false twist of about turns per inch to the yarn with the twist running back toward roll 4. While twistcdfaqueous solution of chloral hydrate was wicked onto the yarn. The weight percent of the chloral hydrate in solution was 80. The wicked yarn contained about 2 weight percent of the solution. The temperature of roll 7 was 220 C.

Then, the yarn was wrapped around roll 4 for the fifth time and was looped back again around heated roll 7 and roll 4 as shown in the drawing. After the third pass around roll 7 the yarn was wound onto a cheese" package on a tubular paper core without twisting the yarn. The windup speed was 725 yards per minute. The tension on the yarn during winding was 10 grams. A small amount of finish was applied to the yarn as it passed over wick 14.

The resulting yarn exhibited excellent physical properties, having a boiling water residual shrinkage of 6.8 percent and an initial modulus of 26 grams per denier. Shrinkage was uniform throughout the package. The paper core on which the yarn was wound did not collapse, whereas the same type core collapsed and could not be removed from the winding spindle without destroying the package when the same yarn drawn by conventional colddrawing was wound thereon. The yarn was used as the warp in the construction of nylon taffeta. The War was prepared and slashed in a conventional manner. The filling was made of nylon filaments untwisted and not treated in accordance with this example. Good coherency of the warp yarn was maintained during the weaving of the fabric; and it dyed uniformly. The yarn had a rotund cross section and was not pronouncedly flat-sided as would be expected from being passed over a surface in the presence of a solvent. The filaments of the yarn were bonded at random points to adjacent filaments and were maintained in substantial parallel relationship.

For determining the residual yarn shrinkage, a skcin of yarn is placed in boiling water for 60 minutes and then is hung up to dry for 24 hours. Percent shrinkage is the initial length of yarn minus the length thereof after boiling divided by the initial length of the yarn times one hundred.

Initial modulus is defined as a ratio of change in stress to strain in the first linear portion of a stress-strain curve. The ratio is calculated from the stress, expressed in force per unit linear density, and the strain expressed as percent elongation. As the strain is expressed in terms of elongation, the modulus equals one hundred times the quotient (stress-strain). The modulus is determined at 1V2 percent elongation based on the slope of the curve at this percentage. The modulus is obtained from yarn stress-strain curves measured by the Instron tensile tester, which, in operation, stretches the yarn at a constant rate of elongation. From the stress-strain curve, the stress is measured graphically at 1 /2 percent elongation on the initial linear portion of the stress-strain curve; and the modulus is calculated at one hundred times this value, divided by the denier of the yarn sample.

Example II The procedure of the above was repeated except an aqueous solution containing 50 weight percent resorcinol was used instead of chloral hydrate. The nylon-66 yarn contained about 1 weight percent of the solution. It Was found that the yarn was relaxed; that is, it was stabilized against longitudinal retraction, having a high initial modulus and low shrinkage. The yarn was suf'liciently coherent that it could be used as warp in the weaving of taffeta without the drawbacks normally encountered when untreated zero .twist yarn is used in the same manner.

Similarly excellent results are obtained when a methanolie solution of 65.5 weight percent resorcinol; an ethanolic solution of 29.9 weight percent hydroquinone; a methanolic solution of 26.4 weight percent hydroquinone; saturated aqueous solution of resorcinol; saturated methanolic solution of pyrogallol, and the like are employed in the treatment of undrawn, untwisted nylon filaments. In each case the yarn is relaxed and adapted for use as warp or filling yarn of a fabric. Other nylons such as nylon-6 can be treated with like results. In addition, acrylic filament yarn with no twist can be treated by the application of an aqueous solution of ethylene carbonate or the like. The yarn is relaxed with the filaments cohered at random points.

The present invention affords numerous advantages. For example, filament yarn can be drawn and relaxed, as well as rendered coherent in one convenient operation. The yarn is stabilized or mitigated against longitudinal retraction such that cheap disposable paper winding cores can be used by filament manufacturers in shipping the yarn to its customer. The yarn can be wound in the form of a tapered package with considerably less occurrence of pirn taper barre. The filaments of the yarn are maintained in substantial parallel relationship, but the yarn has a unifilar character enabling it to perform in the construction of fabric as a coherent unitary strand. The yarn is not excessively fiat as ribbon but exhibits transverse rotundness. Yarns can be processed at high rates, and existing yarn processing apparatus ,can be modified at modest cost to incorporate the novel apparatus features of the present invention. A warp of these yarns can be conveniently slashed by conventional methods.

Since many different embodiments of theinvention can be made without departing from the spirit and scope thereof, the invention is not limited by the specific ilon a lustrations except to the extent defined in the following claims.

What is claimed is:

1. A method of treating molecularly orientable syn thetic continuous multifilament yarn of substantially zero twist comprising the steps:

(a) providing a source of the yarn, the individual filaments of which are substantially straight and parallel;

(b) longitudinally forwarding the yarn;

(c) stretching the yarn by tensioning in a stretch zone to orient the molecules thereof;

(d) reducing the tension on the yarn;

(e) applying a peripheral effort on the yarn to slightly false twist same with the twist running back toward the stretch zone;

(f) coating the false twisted yarn with a small amount of a liquid evanescent solvent thereof;

(g) detwisting the yarn carrying the solvent;

(h) then heating the yarn under low tension to dissipate the action of the solvent and to relax same; and t (i) collecting the yarn in an orderly manner under a tension of about ODS-0.4 gram per denier and at a speed of about 4 to 12% less than the speed of the yarn immediately after being stretched.

2. The method of claim 1 wherein the yarn is made of nylon and the yarn is heated to a temperature of about 150 190 C. in step (11) thereof.

3. The method of claim 2 wherein the solvent is a solution containing about 25-90 weight percent chloral hydrate.

4. The method of claim 2 wherein the solvent is a solution containing about 5-80 weight. percent multi-hydroxybenzene.

5. The method of claim 4 wherein the multi-hydroxybenzene is resorcinol.

6. The method of claim 1 wherein the yarn is an acrylic yarn.

7. The method of claim 6 wherein the solvent is a solution containing about 5-80 weight percent aliphatic cyclic carbonate.

8. The method of claim 1 wherein the yarn is coated with a finish just prior to being collected.

References Cited UNITED STATES PATENTS 2,273,364 2/1942 Mallory 57-I68 X 2,321,726 6/1943 Alderfer 57-168 2,946,181 7/1960 Tissot et a1. 57-157 3,094,834 6/1963 Deeley et .al. 57 157 3,161,706 12/1964 Peters 57-168 X 3,114,235 12/1963 Griset 57--157 FRANK I. COHEN, Primary Examiner.

MERVIN STEIN, Examiner.

J. PETRAKES, Assistant Examiner. 

1. A METHOD OF TREATING MOLECULARLY ORIENTABLE SYNTHETIC CONTINUOUS MULTIFILAMENT YARN OF SUBSTANTIALLY ZERO TWIST COMPRISING THE STEPS: (A) PROVIDING A SOURCE OF THE YARN, THE INDIVIDUAL FILAMENTS OF WHICH ARE SUBSTANTIALLY STRAIGHT AND PARALLEL; (B) LONGITUDINALLY FORWARDING THE YARN; (C) STRETCHING THE YARN BY TENSIONING IN A STRETCH ZONE TO ORIENT THE MOLECULES THEREOF; (D) REDUCING THE TENSION ON THE YARN; (E) APPLYING A PERIPHAL EFFORT ON THE YARN TO SLIGHTLY FALSE TWIST SAME WITH THE TWIST RUNNING BACK TOWARD THE STRETCH ZONE; (F) COATING THE FALSE TWISTED YARN WITH A SMALL AMOUNT OF A LIQUID EVANESCENT SOLVENT THEREOF; (G) DETWISTING THE YARN CARRYING THE SOLVENT; (H) THEN HEATING THE YARN UNDER LOW TENSION TO DISSIPATE THE ACTION OF THE SOLVENT AND TO RELAX SAME; AND (I) COLLECTING THE YARN IN AN ORDERLY MANNER UNDER A TENSION OF ABOUT 0.05-0.4 GRAM PER DENIER AND AT A SPEED OF ABOUT 4 TO 12% LESS THAN THE SPEED OF THE YARN IMMEDIATELY AFTER BEING STRETCHED. 